As motor technology for use in a vehicle and the like as described above, Japanese Patent Laid-Open Publication No. 2000-245085 discloses the use of a concentrated winding, magnet-embedded type motor.
The example disclosed by Japanese Patent Laid-Open Publication No. 2000-245085 will be described in conjunction with FIG. 17. FIG. 17 is a sectional view of a main part of a motor including a concentrated winding stator made of a stator core, a plurality of stator teeth with coils wound therearound, and a magnet-embedded type rotor. The section is a plane orthogonal to the central axis of the rotating shaft of the motor.
As shown in FIG. 17, the stator core 145 includes a plurality of stator teeth 143a, 143b, and 143c, and a stator yoke 144 coupling them. Coils 146a, 146b, and 146c are wound around the stator teeth 143a, 143b, and 143c, respectively and thus the stator 146 is formed. Among the stator teeth 143a, 143b, and 143c, the stator tooth 143a is formed on one side of the stator tooth 143b, the stator tooth 143c is formed on the other side, and thus one group is formed. Groups of such stator teeth 143a, 143b, and 143c are provided in the circumferential direction. The stator teeth 143a each have a coil 146a wound therearound in parallel, the end of the wound coil 146a is connected with a common terminal (not shown), and a single terminating connection line is drawn from the common terminal. The stator teeth 143b each have a coil 146b wound therearound in parallel, and the stator teeth 143c each have a coil 146c wound therearound in parallel. The terminating connection lines for the stator teeth 143a, 143b, and 143c are each connected to another common terminal (not shown).
The rotor 147 has a plurality of permanent magnets 149 embedded at equal intervals in the circumferential direction so that these magnets oppose the inner circumferential surfaces of the stator teeth 143a, 143b, and 143c of the stator 146. The rotor 147 has its outer circumferential surface opposed to the inner circumferential surfaces of the stator teeth 143a, 143b, and 143c of the stator 146 with a very small gap therebetween. The distance between the surfaces 149a of the permanent magnets 149 that oppose the inner circumferential surfaces of the stator teeth 143a, 143b, and 143c and the outer circumferential surface of the rotor 147 is larger toward the central part 149c than at the ends 149b of the permanent magnet 149.
The coils 146a, 146b, and 146c form three phases, or a U phase, a V phase, and a W phase, respectively, and when currents in trapezoidal waveforms for example 120 electrical degrees out of phase between each other are provided to the coils in these phases, and torques generated between the coils 146a, 146b, and 146c in these phases and the rotor 147 are 120 degrees out of phase between each other. The torques in the three phases are combined to form a total torque, and the rotor 147 rotates in a prescribed direction accordingly. More specifically, so-called three phase, full wave-driven rotation around the center O of the rotating shaft is carried out. Therefore, in addition to the magnetic torque resulting from the embedded permanent magnets 149 in the rotor 147, a reluctance torque can also be used, so that a high output (high torque) motor that generates a large torque can be provided.
Meanwhile, when the rotor 147 is driven to rotate, a counter electromotive voltage in a substantial sine wave is generated between a common terminal (not shown) and the U, V, and W phase terminals according to the Flemming's right hand rule. As is well known, the counter electromotive voltages for the phases are 120 electrical degrees out of phase among each other, and the counter electromotive voltages in the different phases are combined to obtain a total counter electromotive voltage.
For environmental concerns and resource conservation, there is a demand for use of less copper coils in vehicle motors in general. In the process of recycling automobiles, motors with copper wires mixed with other motors deteriorate the quality level of recycled iron, and in the field of automobiles, motors with copper-free wires are strongly desired. According to conventional techniques, aluminum wires are used for coils for motors instead of copper wires, or aluminum wires are used for other general commutator coils instead of copper wires as disclosed by Japanese Patent Laid-Open Publication No. 2000-245085. However, examples of actual application of the disclosed methods to automobiles have not been known.
The motor with a large torque including the additional reluctance torque can advantageously have a high torque by employing a concentrated winding motor. On the other hand, waveform distortions are observed in the counter electromotive voltage.
A large waveform distortion in the counter electromotive voltage increases eddy current and thus iron loss, which lowers the efficiency. Eddy current is also generated at the permanent magnets embedded in the rotor, and the permanent magnets generate heat to have increased temperature, and could be demagnetized.
Therefore, it is a first object of the invention to provide a high torque, high efficiency motor in a structure with reduced waveform distortions in the counter electromotive voltage and with reduced eddy current generation.
Meanwhile, if coils for a motor as disclosed by Japanese Patent Laid-Open Publication No. 2000-245085, a typical commutator motor and a brushless motor are simply changed from copper wires to aluminum wires, the conductor loss could be great because the resistivity of the aluminum wire is higher than copper wire by about 60%. Therefore, the efficiency of the motor is lowered. Meanwhile, in order to keep the loss from increasing, the motor size must be increased, and in either way, the method remains to be disadvantageous in terms of energy and resource conservation.
It is a second object of the invention to provide a motor with coils made of aluminum or another metal having resistivity larger than copper instead of copper without increasing the size of the motor and lowering the efficiency while the first object is achieved as well.